The present invention relates to ground fault circuit interrupting (GFCI) devices and particularly to an integrated circuit therefor having improved operational coordination.
GFCI devices are presently enjoying wide use in certain residential circuits, on construction sites and in industry to protect personnel from potentially injurious electrical shock should they become involved in line-to-ground fault. These devices are available in either a circuit breaker configuration acceptable in a conventional circuit breaker load center or a receptacle configuration acceptable in a conventional wall outlet box. To achieve their acceptability in such existing facilities, GFCI devices must be dimensionally comparable to conventional circuit breakers and outlet receptacles lacking ground fault protection capability. Consequently, the components operating to afford ground fault protection must be highly miniaturized to accommodate being packaged in very little available space. Thus, the requisite electronics should be implemented in integrated circuit form. Discrete circuit components should be as compact in size and few in number as possible. The cores of the requisite differential current transformer and double ground neutral excitation transformer must also be quite small.
Since, in both the GFCI breaker and receptacle configurations, the components are housed in a molded insulative case, power consumption of the electronic circuit components must be kept very low in order to minimize internal temperature rise. As is well understood, heat has a particularly detrimental effect on the reliability, stability and life of electronic elements, whether in discrete or integrated circuit form. Another particularly perplexing problem area brought on to a considerable extent by the requisite miniaturization, the solution to which being complicated by space limitations, is nuisance tripping occasioned by spurious responses to noise. A typical residential circuit is found to carry considerable high frequency noise and high voltage transients for which measures must be taken to reject or bypass from the GFCI electronics if nuisance tripping is to be avoided.
Intimately tied in with the above-noted and other GFCI design considerations is manufacturing expense. That is, reliable GFCI devices must be made available at a reasonable cost to the buying public in order to encourage wider use and thus further reduce the instances of electrical shock injury to humans.
It is accordingly an object of the present invention to provide an improved GFCI device.
A further object is to provide a GFCI device of the above character wherein its electronic circuit operation is coordinated in a manner to reduce power consumption and increase reliability.
Another object is to provide a GFCI device of the above character which has enhanced noise immunity and thus a minimized propensity to nuisance trip.
An additional object is to provide a GFCI device of the above character which is inexpensive to manufacture and reliable in operation.
Other objects of the present invention will in part be obvious and in part appear hereinafter.